Transmembrane β-barrel proteins

Publisher Summary The major fraction of transmembrane proteins is α-helical—their β-barrel counterparts have become popular because many of them could be analyzed in atomic detail and at high resolution. The transmembrane β-barrel proteins occur only in the outer membranes of bacteria, mitochondria, and chloroplasts. They assume astonishingly regular conformations giving rise to numerous rules for their construction. It has been suggested that these regularities are required by the folding process. They are likely to permit the detection of transmembrane β-barrels from the sequence at a reasonable confidence level in the future. The main chain amides of α-helices are all locally complemented so that the interface to the nonpolar membrane interior is exclusively formed by the nonpolar side chains. This explains the usefulness of an α-helix as a membrane-crossing element.